The present invention relates to a vehicle forced-induction device in which two forced-induction units are arranged in series.
Japanese Laid-Open Patent Publication No. 2012-012990 discloses a vehicle forced-induction device that includes a first forced-induction unit and a second forced-induction unit, which are arranged in series. In the forced-induction device, the first forced-induction unit includes a first turbine housing for housing a turbine, and the second forced-induction unit includes a second turbine housing for housing a turbine. The first turbine housing and the second turbine housing each include an inlet pipe for introducing exhaust gas and an outlet pipe for discharging exhaust gas to the outside. The distal end of the outlet pipe of the first turbine housing and the distal end of the inlet pipe of the second turbine housing each have a flange. Then, these flanges are fastened together with bolts in a state in which the end face of the distal end of the outlet pipe of the first turbine housing and the end face of the distal end of the inlet pipe of the second turbine housing, so that the outlet pipe of the first turbine housing and the inlet pipe of the second turbine housing are connected to each other. In the forced-induction device disclosed in the above publication, the flanges are fastened together with an intermediate member, which has a valve, placed in between. By arranging the two forced-induction units in series in this way, the exhaust gas discharged from the first turbine housing is introduced into the second turbine housing.
In the above structure, in which two flanges face each other and are fastened together with bolts, each flange needs to have bolt insertion holes. The existence of the bolt insertion holes inevitably increases the dimension of each flange in the radial direction from the central axis of the outlet pipe and the inlet pipe.